Some Christians are taking to Twitter and Instagram to share selfies in observance of Ash Wednesday, tagging photos and tweets with #ashtag.  

Ash Wednesday marks the beginning of Lent, the 40 days of fasting and repentance before Easter. Those attending morning mass are given a cross sign in ashes on their foreheads to symbolize penance, mourning and mortality.  

"Did you join us in placing the Cross on your forehead tonight?" tweeted Northfield Church. "We'd love to see your #Ashtag."

A search of #ashtag on Twitter returns pictures of smiling people showing off their foreheads, including priests, sisters, and even Rick Santorum sharing selfies.

"We got our ashes in Church today!" tweeted Santorum with a selfie of him and his wife, Karen.  

However, not everyone has been happy about the trend.  

"I'm not liking this whole #ashtag selfie thing," tweeted one user. "It feels a little weird... is that just me?"

"Don't commoditize Ash Wednesday," said Twitter user Brandon Vogt. "Don't exchange the sacred for the #Ashtag selfie."

Twitter user Jacob Lupfer explained the controversy through the Bible, tweeting, "Matt 5:16 'Let your light so shine before men,' vs. Matt 6:15 'No reward in having others see your devotion.'"